Greater intake of long-chain omega-3 fatty acids (EPA and DHA) is associated with decreased risk of brain disorders (such as Alzheimer’s disease) and cardiovascular disease.1-3 DHA is a crucial factor in early brain development because it is a major constituent of cell membranes in the brain, retina, and nervous system. There is significant evidence in the fossil record that a increase in DHA availability in the diet of early humans was responsible for the expansion of the brain into the large, complex organ it has now become.4,5 DHA requirements are the greatest in the developing brain during the last trimester of pregnancy and the first two years of life. During early life, a baby’s only source of this building block of brain and eye tissue is its mother’s milk.6,7 Several studies have documented improved cognitive scores in breastfed infants compared to formula-fed infants, prompting supplementation of infant formula with DHA in the U.S.8 But what if the “normal” amount of DHA in American women’s breast milk is still not enough? What if the developing brain requires more DHA for optimal cognitive development?
A recent study compared the fatty acid content of breast milk in American women in Cincinnati to that of Tsimane women of Bolivia. Tsimane women eat a traditional diet of primarily locally grown plant foods, wild-caught animals, and freshwater fish. The results of the study showed that the DHA concentration of Tsimane mothers’ milk was 400% higher than that of Cincinnati mothers, their concentration of linoleic acid (an omega-6 fatty acid abundant in oils) was 84% lower, and their concentration of trans fat was 260% lower than in Cincinnati mothers.9,10 In a previous analysis, pooling data from 84 studies of breast milk DHA concentrations in many different countries, the U.S. concentrations fell below the worldwide average. The areas with the highest breast milk DHA concentrations were coastal or island nations, suggesting that breast milk DHA concentration is closely linked to the consumption of fish.11
Our modern eating habits have transformed the fatty acid distribution of our diet.12 One of the study’s authors, Steven Gaulin, a professor of anthropology at the University of California at Santa Barbara, noted "The American diet is eroding one of the most important benefits breast milk can provide –– fats that are critical to infant brain development. It's not surprising that, among developed nations, American children are last on international tests of math and science."9
What is the “normal” DHA of content of human breast milk – or rather, the amount that will ideally support brain development in infants? We don’t know for sure. However, these huge differences between a traditional diet and a modern diet, and the high DHA concentrations in high fish-consuming countries indicate that the DHA intake of Americans may be sub-optimal for supporting brain health. The American diet is low in DHA, and high in vegetable oils and trans fats, which limit the elongation of ALA from plant foods into DHA and EPA, and displaces omega-3 fats from cell membranes.4,13 Factory-farmed meats, oils and trans fats are not the appropriate fatty fuel to grow a baby’s brain.
Does this mean that we should eat fish? From the evidence we have now, if you eat with a modern diet (even without oils) and you don’t eat fish regularly, it is almost impossible to have adequate DHA stores, especially for pregnant and nursing women.
Avoiding oils and eating plenty of hemp, chia, flax, walnuts, and leafy greens is likely still not enough, since the conversion rate of ALA (short-chain omega-3) in these foods to DHA (long-chain omega-3) is very low. Large increases in ALA intake have been shown to produce only very slight increases in long-chain omega-3 blood levels. Plus, much of the ALA we consume is burned for energy, not converted to DHA or EPA.14,15
However, modern fish is a heavily polluted food that I do not recommend eating regularly. The DHA in fish may benefit the brain, but the fatty tissues of fish is highly contaminated with mercury, and other pollutants, which could be toxic to the brain and may also contribute to cardiovascular disease.16,17 In addition to the potential effects of mercury on human health, huge declines in wild fish populations have been reported since the 1950s, and populations continue to decline as the purported benefits of fish consumption on heart and brain health increase the demand for fish and fish oils.18 Fish is not an ideal source of DHA; fortunately DHA derived from lab-grown algae is available as a supplement.
One can't really be sure they have ideal levels of omega-3 anymore without supplements. If you eat enough fish to idealize your omega-3 ratio, you get too much mercury, dioxin, and other pollutants. I think it is sensible and conservative to err on the side of caution and eat a diet that contains ALA from flax, chia, walnuts and leafy greens, not merely because of their ALA content, but also for their anti-inflammatory and anti-cancer effects. Then adding a supplement of a clean algae-derived DHA is a wise insurance policy. Significant evidence suggests that a comparatively small amount of DHA and EPA can add health protection without the potential drawbacks of high dose fish oil capsules.19-21
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9. UCSB anthropologists finds high levels of omega-3 fatty acids in breast milk of Amerindian women. 2012. EurekAlert! http://www.eurekalert.org/pub_releases/2012-06/uoc--uaf060812.php. Accessed August 15, 2012.
10. Martin MA, Lassek WD, Gaulin SJ, et al. Fatty acid composition in the mature milk of Bolivian forager-horticulturalists: controlled comparisons with a US sample. Matern Child Nutr 2012;8:404-418.
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12. Blasbalg TL, Hibbeln JR, Ramsden CE, et al. Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century. Am J Clin Nutr 2011.
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14. Arterburn LM, Hall EB, Oken H. Distribution, interconversion, and dose response of n-3 fatty acids in humans. Am J Clin Nutr 2006;83:1467S-1476S.
15. Fokkema MR, Brouwer DA, Hasperhoven MB, et al. Short-term supplementation of low-dose gamma-linolenic acid (GLA), alpha-linolenic acid (ALA), or GLA plus ALA does not augment LCP omega 3 status of Dutch vegans to an appreciable extent. Prostaglandins Leukot Essent Fatty Acids 2000;63:287-292.
16. Rice GE, Hammitt JK, Evans JS. A probabilistic characterization of the health benefits of reducing methyl mercury intake in the United States. Environmental science & technology 2010;44:5216-5224.
17. Virtanen JK, Rissanen TH, Voutilainen S, et al. Mercury as a risk factor for cardiovascular diseases. The Journal of nutritional biochemistry 2007;18:75-85.
18. Myers RA, Worm B. Rapid worldwide depletion of predatory fish communities. Nature 2003;423:280-283.
19. Musa-Veloso K, Binns MA, Kocenas A, et al: Impact of low v. moderate intakes of long-chain n-3 fatty acids on risk of coronary heart disease. Br J Nutr 2011.
20. Thies F, Nebe-von-Caron G, Powell JR, et al. Dietary supplementation with eicosapentaenoic acid, but not with other long-chain n-3 or n-6 polyunsaturated fatty acids, decreases natural killer cell activity in healthy subjects aged >55 y. Am J Clin Nutr. 2001 Mar;73(3):539-48.
21. Linus Pauling Institute: Essential Fatty Acids. http://lpi.oregonstate.edu/infocenter/othernuts/omega3fa/